The present invention relates to power screwdrivers in general, and more particularly to hand-held torque limiting power screwdrivers.
There are already known various constructions of power tools, such as power screwdrivers, which are so constructed as to limit the torque which can be exerted thereby on a screw or a similar threaded fastener. One such conventional power tool is disclosed in the German Pat. No. 1,678,656. This power tool includes a screwdriver spindle which is rotatably and axially displaceably mounted in a housing, a separating coupling which becomes engaged and disengaged in response to the axial movement of the screwdriver spindle so as to respectively establish and interrupt power transmission between a motor and the screwdriver spindle, and a torque overload coupling which is operative for interrupting the power transmission.
This conventional construction has the disadvantage that the range of operation thereof terminates at approximately 25 Nm of resistance torque when used in one-hand screwdriving operation. Impacting power screwdrivers are being used for the tightening of screws which require higher tightening torques; however, such impacting power screwdrivers generate a substantial amount of noise. There are also already known angular power screwdrivers which are capable of exerting higher torques. However, such angular power screwdrivers are not suited for the use of the proven combination of a separating coupling with a torque overload coupling, since it is not possible in such conventionally constructed angular power screwdrivers to simply operate the separating coupling during the application of the power screwdriver to the screw by longitudinally displacing the screwdriver spindle.